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141.
G. V. Girichev N. V. Tverdova S. A. Shlykov V. V. Rybkin N. P. Kuzmina A. Yu. Rogachev 《Journal of Structural Chemistry》2006,47(6):1071-1077
In a mass spectrometric study, it was found that the saturated vapor over gadolinium tris-hexafluoroacetylacetonate Gd(C5O2HF6)3 contains molecular forms with a mass exceeding the mass of the dimer. The vapor overheated to 250–300°C contains only the monomer form. Simultaneous electron diffraction and mass spectrometric experiment aimed at investigating the structure of the Gd(hfa)3 monomer molecule was carried out at 284(5)°C. The Gd(hfa)3 molecule was found to have the symmetry of the equilibrium D 3 configuration. The basic structural parameters are r h1(Gd-O) = 2.291(10) Å, r h1(O-C) = 1.257(10) Å, r h1(C-Cr) = 1.404(6) Å, r h1(CF-F)av = 1.341(3) Å, ∠OGdO = 72.8(0.4)°. The GdO6 coordination polyhedron has the structure of a distorted antiprism. The rotation angle of the O-O-O trigonal faces relative to their position in a regular prism is 18.7(0.9)°. Quantum chemical calculations (HF/SBK, 6-31G*) generally reproduce the experimental structure, but the Gd-O internuclear distance is exaggerated by 0.04 Å. 相似文献
142.
143.
The effect of a roughening procedure on surface-enhanced Raman scattering (SERS) intensity of pyridine at copper and gold electrodes subjected to negative potential has been investigated. Among four procedures tested for a copper electrode the one consisting of electrochemical activation in a solution of LiCl and CuCl2 resulted in the most stable and effective surface. It was proved that the presence of pyridine during the pretreatment procedure caused a very fast, irreversible decay of SERS intensity for both copper and gold electrodes. Quite stable, at least at room temperatures, gold surfaces were obtained by oxidation-reduction cycles activation in KCl solution. 相似文献
144.
Mateja
ikovec Mladen Franko Federico G. Cruz Sidney A. Katz 《Analytica chimica acta》1996,330(2-3):245-250
The applicability of thermal lens spectrometry (TLS) for quantification and routine determination of hexavalent chromium was investigated by using a collinear dual beam thermal lens spectrometer. In aqueous solutions the LOD of 0.1 μg l−1 was obtained for Cr(VI) by using 160 mW laser power. The performance of the technique was verified by the determination of hexavalent chromium in standard reference water samples (NIST SRM 1643a and NIST SRM 1643c) and comparing the results for Cr(VI) in CCA (Cr, Cu, As)-treated timber extracts to concentrations obtained by atomic absorption spectrometry (AAS). Good agreement between the TLS results and reported values for Cr(VI) in SRMs as well as AAS results for Cr(VI) in CCA-treated timbers confirmed that TLS is a reliable and accurate analytical technique applicable for the determination of Cr(VI) in aqueous solutions at concentration levels 0.5–100 μg l−1. 相似文献
145.
Summary The aim of this investigation was to obtain qualitative and quantitative profiles of the flavonoid and biflavonoid composition
of six cypress species—Cupressus funebris L.,Cupressus sempervirens L.,Cupressus glabra L.,Cupressus arizonica L.,Cupressus goveniana L., andCupressus lusitanica L. HPLC-diode-array detection (DAD), HPLC-MS, and HPTLC were used to identify the individual compounds. A chromatographic
method was optimized for identification and quantification of the main flavonoid glycosides and biflavonoids. The flavonoids
identified and calibrated were: rutin, quercetin glucoside, quercetin rhamnoside, and kaempferol 3-O-rhamnoside. The biflavonoids identified and calibrated were: cupressuflavone, amentoflavone, robustaflavone, hinokiflavone,
methylrobustaflavone, methylamentoflavone, and dimethylcupressuflavone. 相似文献
146.
Analytical procedures for quantification of peptides in pharmaceutical research by liquid chromatography–mass spectrometry 总被引:6,自引:0,他引:6
John H Walden M Schäfer S Genz S Forssmann WG 《Analytical and bioanalytical chemistry》2004,378(4):883-897
Peptide quantification by liquid chromatography–mass spectrometry (LC–MS) combines the high resolving power of reversed-phase (RP) chromatography with the excellent selectivity and sensitivity of mass spectrometric detection. On the basis of comprehensive practical experience in the analysis of small molecules, pharmaceutical research is developing technologies for analysis of a growing number of peptidic drug candidates. This article is a detailed review of procedures based on LC–MS techniques for quantitative determination of peptides. With the focus on pharmaceutical applications several technologies for sample preparation, various aspects of peptide chromatography, important characteristics of ESI–MS, selectivity of MS-detection modes, the large variability of internal standards, and modern instrumentation are discussed. The demand for reliable, robust, sensitive, and accurate methods is discussed using numerous examples from the literature, complemented by experiments and results from our laboratory. 相似文献
147.
Tomazela DM Gozzo FC Mayer I Engelmann FM Araki K Toma HE Eberlin MN 《Journal of mass spectrometry : JMS》2004,39(10):1161-1167
Ten homologous or isomeric singly, doubly, triply and quadruply charged cationic macrocyclic complexes I-Va, bn+ (n = 1-4) formed by the coordination of [Ru(bipy)2Cl]+ to the pyridyl N-atoms of a series of meso-(phenyl)m-(meta or para-pyridyl)n-porphyrins (m + n = 4) were transferred to the gas phase and structurally characterized by electrospray ionization (ESI) mass (MS) and tandem mass (MS/MS) spectrometry. Previously known to be stable in solution and in the solid state, I-Va, bn+ are found to constitute also a new class of stable, long-lived multiply charged gas-phase ions with spatially separated charge sites. Increasing intramolecular electrostatic repulsion from Ia, b+ to IVa, b3+ facilitates in-source and tandem collision-induced dissociation (CID). However, for the quadruply charged ions Va, b4+, electrostatic repulsion is alleviated mainly by ion pairing with the CF3SO3- counterion forming the salt clusters [Va,b/CF3SO3]3+ and [Va,b/(CF3SO3)2]2+ with reduced charge states. Ion-pairing that yields [IVa,b/CF3SO3]2+ is also observed as a minor ESI process for the triply charged ions IVa, b3+. The gaseous ions I-Va, bn+ (n = 2, 3 or 4) dissociate by sequential 'charge partitioning' with the formation of two cationic fragments by the release of [Ru(bipy)2Cl]+. The meta (a) and para (b) isomers and the positional isomers II2+ and III2+ display nearly identical ESI-MS and ESI-MS/MS spectra. ESI-MS/MS of I-Va, bn+ shows that the Ru-py(P) is, intrinsically, the weakest bond since this bond breaks preferentially upon CID. 相似文献
148.
采用二硫化碳重结晶富勒烯混合物或二硫化碳二次抽提烟灰以提取高富勒烯(higherfulerenes,Cn,n>70)。产物经高效液相色谱分析,高富勒烯的含量从1%分别提高到4%和6%;经激光飞行时间质谱证明,产物中除含主要成分C60和C70以外,还含有C76、C78、C82、C84以及更高碳原子的富勒烯。 相似文献
149.
Based on carbon nanofibers (CNFs) as a solid phase extraction adsorbent, a microcolumn preconcentration method coupled to inductively coupled plasma mass spectrometry (ICP–MS) was developed for the determination of trace elements (Mn, Co and Ni). The effect of various experimental parameters such as pH, sample flow rate and volume, elution solution and interfering ions on the retention of the studied ions have been investigated systematically. During all the steps of the experimental process, Mn, Co and Ni could be quantitatively sorbed on the microcolumn containing CNFs in the range of pH 6.0–9.0, and then eluted completely with 0.5 mol ml− 1 HNO3. A preconcentration factor of 150-fold was obtained. The detection limits for Mn, Co and Ni were 40, 0.4 and 8.0 pg ml− 1, respectively, with relative standard deviations less than 6.0%. In order to validate the proposed method, two certified reference materials of human hair (GBW 07601) and mussel (GBW 08571), and water sample were analyzed with satisfactory results. The recoveries were between 95.0 and 114%. 相似文献
150.
Samuel K Yin W Stearns RA Tang YS Chaudhary AG Jewell JP Lanza T Lin LS Hagmann WK Evans DC Kumar S 《Journal of mass spectrometry : JMS》2003,38(2):211-221
Metabolic activation of drug candidates to electrophilic reactive metabolites that can covalently modify cellular macromolecules may result in acute and/or idiosyncratic immune system-mediated toxicities in humans. This presents a significant potential liability for the future development of these compounds as safe therapeutic agents. We present here an example of an approach where sites of metabolic activation within a new drug candidate series were rapidly identified using online liquid chromatography/multi-stage mass spectrometry on an ion trap mass spectrometer. This was accomplished by trapping the reactive intermediates formed upon incubation of compounds with rat and human liver microsomes as their corresponding glutathione conjugates and mass spectral characterization of these thiol adducts. Based on the structures of the GSH adducts identified, potential sites and mechanisms of bioactivation within the chemical structure were proposed. These metabolism studies were interfaced with iterative structural modifications of the chemical series in order to block these bioactivation sites within the molecule. This strategy led to a significant reduction in the propensity of the compounds to undergo metabolic activation as evidenced by reductions in the irreversible binding of radioactivity to liver microsomal material upon incubation of tritium-labeled compounds with this in vitro system. With the efficiency and throughput achievable with such an approach, it appears feasible to identify and address the metabolic activation potential of new drug leads during routine metabolite identification studies in an early drug discovery setting. 相似文献